BERLIN, June 29 (Xinhua) -- Cooperation between German intelligence services and the U.S. National Security Agency (NSA) is deeper than previously believed in the fight against terrorism and laws have been ignored in this process, a NSA whistleblower told Sunday to German newspaper Die Welt.

Thomas Drake, a former senior executive of the NSA, is expected to give testimony next week at a committee of the Bundestag, the lower house of German parliament, which is inquiring into U.S. spying activities in Germany.

The 57-year-old U.S. citizen told Die Welt that he has "dirty knowledge" and will reveal "specific information" about the cooperation between the NSA and the German intelligence service BND.

He said there had been "extremely broad" agreements between the NSA and the BND, adding that their intelligence cooperation takes "precedence over everything else and overrides all restrictions placed by the respective constitution".

Drake began to work for the NSA after the Sept. 11 attacks, developing espionage programs for the intelligence agency.

In 2006, he leaked information about the NSA's data-gathering Trailblazer Project to an American newspaper. He allegedly "mishandled" documents and was prosecuted under the Espionage Act in 2010, but the case collapsed.

Drake is now living in the United States. He has become the most important testifier to the German NSA inquiry panel after a testimony of Edward Snowden in Germany was blocked.

New allegations regarding U.S. surveillance continue to be brought forward.

According to a report recently published by German media, the NSA had been given access to large swaths of telecoms data by the BND. For at least three years raw data was fed directly to the NSA from Germany's Frankfurt on the Main -- the city is a telecoms hub for much of Europe and beyond.